Conventionally, there is a radio communication system including base station apparatuses and mobile terminal apparatuses connected by radio to the base station apparatuses. Each of the base station apparatuses forms a coverage area (cell) where the base station apparatus can communicate with terminal apparatuses. The terminal apparatuses located in the cell can perform radio communication with the base station apparatus forming the cell (see, for example, Patent Literature 1).
In the above-described radio communication system, when coverage areas (cells) set by a respective plurality of base station apparatuses overlap with each other, a signal transmitted from a base station apparatus may reach a terminal apparatus in a cell of another base station apparatus near the base station apparatus and thus become an interference signal to the terminal apparatus.
Furthermore, the above-described radio communication system includes, as base station apparatuses, for example, a macro base station apparatus that forms a cell (macrocell) of several kilometers in size; and a femto base station apparatus that is installed in the macrocell and forms a relatively small cell (femtocell) of the order of several tens of meters in the macrocell. In this radio communication system, since substantially the entire area of the femtocell formed by the femto base station apparatus overlaps with the macrocell, it can be said that this environment easily causes interference therebetween.
For the methods of suppressing interference waves under such an environment, measures such as keeping the transmission power on the interference giving side at a low level and removing interference waves by a multi-antenna system are considered.
Of them, for the method of removing interference waves by a multi-antenna system, as shown in the following Patent Literature 2, the application of which is filed by the inventors of the present invention, there is a method in which a weight is calculated on a per minimum unit of radio resource allocation basis, whereby a weight is calculated based only on signals received from the same user. According to this method, since the number of interfering sources in the minimum unit is limited, an appropriate weight can be obtained and thus removal of interference waves can be effectively performed.